1. Field of the Invention
The invention relates to a power factor correction device. In particular, the invention relates to a power factor correction device including electronic ballast function, which adds a control circuit to produce the electronic ballast action to reduce harmonic interference, save power and space, and increase system reliability.
2. Description of the Related Art
Electronic ballast power factor refers to an efficient power percentage of an input current actually used in an electronic ballast circuit. In general, an electronic ballast circuit driven by the high-frequency voltage to light a lamp has a higher light output, i.e., to save more power. Hence, the electronic ballast circuit is in widespread use, e.g., various projectors, to replace the conventional ballast circuit and starter. Typically, a projector""s lamp lighting circuit separates a power factor correction converter and an electronic ballast circuit as shown in FIG. 1. FIG. 2 is a circuit diagram of a conventional ballast system. In FIG. 2, the system includes a rectifier 21, a power factor correction (PFC) circuit 22, an energy storing capacitor C3, an electronic ballast circuit 24, an ignitor 25 and a lamp. The rectifier 21 includes a full-bridge rectifier comprised of diodes BD1-BD4 to produce a DC output, for example, converting 110 VAC into 150 VDC or 220 VAC into 300 VDC, and a filter capacitor C1 to filter the DC output in order to avoid noise interference coming from rectifier 21. The PFC circuit 22 mainly includes a transformer T1, start resistors R1, R2, a T1-waveform sensing resistor R3, an integrating filter capacitor C2, a block diode D1, a metal-oxide-semiconductor field-effect transistor (MOSFET) switch Q1 and a controller CTRL1. The output of the rectifier 21 is coupled to an end of the start resistor R1 and an end of a first inductor TL1 of the transformer T1. Another end of the start resistor R1 is coupled to an end of the start resistor R2. Another end of the first inductor TL1 is coupled to the source of the switch Q1 and a forward-biased diode D2. Another end of the start resistor R2 is coupled to the input of the controller CTRL1, the grounding integrating filter capacitor C2, and the reverse end of the block diode D1 (node A). The forward end of the block diode (node B) is coupled to an end of the resistor R3 and an end of a second inductor TL2 of the transformer T1. Another end of the second inductor TL2 is to the ground. Another end of the sensing resistor R3 is coupled to the input of the controller CTRL1. The output of the controller CTRL1 is coupled to the gate of the switch Q1 through a resistor R4. The drain of the switch Q1 is coupled to the input of the controller CTRL1 and a grounding resistor R5. In such a configuration, the circuit 22 uses the controller CTRL1 to receive the output voltage sensing from the transformer T1 by the resistor R3 and a feedback signal FB from the drain of the switch Q1. The feedback signal FB is used to modify the output voltage from the two inductors of the transformer T1 to selectively change the ON duty ratio and/or the frequency of the switch Q1 so as to output a correct power factor. The block diode D1 blocks the reserve current from the capacitor C2 discharge to avoid affecting the sensing value of the sensing resistor R3. Hence, the controller cannot output the correct power factor. Similarly, the diode D2 has the same block function as the grounding capacitor C3 storing the DC output from the PFC circuit 22. The load condition will influence the output phase coherence of the current and voltage, for example, in a projector with an incandescent lamp only able to have the same output phase on the voltage and current and the 100% output power factor. However, in practical, load is more complicated, such as, for example, when a high voltage mercury lamp is used, a capacitor (C3) to store the power and an electronic Ballast to keep the power factor output in a steady state, for example, over 0.95, are a must. Typically, as shown in FIG. 2, the circuit 24 includes an MOSFET switch Q2, a shunt LC resonant circuit, a block diode D3 and a controller CTRL2. The source of the switch Q2 connects to the free end of the capacitor C3, the gate to an input signal from the controller CTRL2 through the resistor R6, the drain to the reverse end of the diode D3 and an end of the inductor L1 in the shunt LC circuit. The inductor L1 connects to an end of an external lamp LAMP and the free-end of the grounding capacitor C4 in the shunt LC circuit. The forward end of the diode D3 connects the ground and an end of the resistor R7. Another end of the resistor R7 connects to the controller CTRL2 to produce a feedback signal BFB. Another end of the resistor R7 also connects to an end of the ignitor 25 including a transformer T2 to ignite and a controller CTRL3 to control the transformer T2. Another end of the ignitor 25 connects another end of the lamp LAMP. The controller CTRL2 outputs a control signal to adjust the Q2 output frequency based on the feedback signal BFB, so as to control the output power from the LC resonant circuit having the DCxe2x80x94DC conversion function to the lamp LAMP. The diode D3 having the same function as mentioned the diode D1 above can avoid the feedback signal affected by the reversed current and voltage from the drain of the switch Q2. Further, the reversed current and voltage influence the voltage supply to the lamp LAMP, so as to affect the lighting (projecting) stability of the lamp (i.e., Flicker Index (FI) for light). For example, the lamp""s FI over 0.01 can cause vibration on the projecting frame. To solve this problem, the PFC circuit 22 typically keeps the output voltage of the rectifier 21 around 380 VDC and decreases the output voltage to about 85 VDC by the LC resonant circuit in the ballast circuit 24 to provide the lamp LAMP the required voltage. However, this makes the circuitry complicated so as to waste power, space and cost.
Accordingly, an object of the invention is to provide a power factor correction device including electronic ballast function, which adds a control circuit to produce the electronic ballast action to reduce harmonic interference, save power and room, and increase system reliability.
The invention provides a power factor correction device including electronic ballast function. The device includes a lamp; an ignitor, connected in series with the lamp, to start the illumination; a voltage and current controller, connected in parallel with the cascade lamp and ignitor, to receive the voltage across the lamp and output a feedback signal according to the received voltage; and a power factor correction (PFC) circuit, connected in parallel with the voltage and current controller, to adjust an output power according to the feedback signal to protect the circuit and increase the stability.